Urethane adhesives are used for bonding automotive fiberglass reinforced parts. One such adhesive is U.S. Pat. No. 4,876,308 to Melby et al. which teaches that an NCO:(OH+NH) ratio of at least 1.2 and desirably 1.35 is advantageous to eliminate the need for primers. U.S. Pat. No. 5,175,228 to Wang et al. also relates to urethane adhesives. It additionally teaches that phosphorus adhesion promoters and isocyanate trimerization catalysts in adhesives with a NCO:(OH+NH) ratio of at least 1.2 can result in better adhesion after high temperature bakes. The trimerization catalyst is assumed to trimerize the excess unreacted isocyanates. A drawback with these compositions was the lack of adhesion of certain paints or primers to any exposed adhesive after part assembly and cure.
It is the object of this invention to provide an adhesive that better retains paint. Another object of the invention is to provide a urethane adhesive having primerless adhesion and high temperature resistance when the equivalent ratio of NCO:(OH+NH) is below 1.2.